1. Technical Field
This invention generally relates to monitoring devices for pneumatic tires and, more particularly, to a monitoring device having a dipole antenna used to monitor at least one engineering condition of a tire and to transmit information relating to the engineering condition to an information-gathering device positioned outside of the tire. Specifically, the present invention relates to a monitoring device having a radial dipole antenna mounted on the inside of a pneumatic tire and arranged orthogonally to the lines of electrical interference in the tire sidewall so that the probability of signal propagation through the tire sidewall is improved.
2. Background Information
It is desired in the art to monitor the conditions of a pneumatic tire while the tire is installed and in use on a vehicle. Although it is desirable to monitor engineering conditions of passenger car tires as well as truck and bus tires, it is particularly desirable to monitor the conditions of off-the-road tires because of the relatively high cost of the tires and the desire to prevent down time from a tire failure. Measuring the engineering conditions of a tire preferably occurs while the tire is in use on the off-the-road vehicle without having to remove the tire from the vehicle or specifically position the tire to take the measurements. Measuring the engineering conditions in this manner prevents the vehicle from being removed from service and thus increases the efficiency of the vehicle. Furthermore, by indicating when a tire is under-inflated, it allows prompt re-inflation to correct pressure which increases tire life providing an economic benefit.
Numerous types of monitoring devices are known in the art to perform these measurements. One type of monitoring device uses a passive integrated circuit imbedded within the body of the tire that is activated by a radio frequency transmission that energizes the circuit by inductive magnetic coupling. Other prior art devices used for monitoring tire conditions include self-powered circuits that are positioned external of the tire, such as at the valve stem. Other active self-powered programmable electronic devices are disclosed in U.S. Pat. Nos. 5,573,610, 5,562,787, and 5,573,611 which are assigned to the assignee of the present application.
Each of the active self-powered programmable electronic devices includes an antenna that is used to transmit the information gathered by the monitoring device to the information-gathering device positioned outside of the tire. One of the problems in the art is to position and configure the antenna such that the data created by the monitoring device are accurately transmitted to the information gathering device outside of the tire. In many multi-point communication systems, linearly polarized antennas are used to transmit the information gathered by the monitoring device to the information-gathering device. It is known in the art that misalignment between the sensitive access of the antennas will result in a polarization mismatch and thus a reduction in system communications efficiency. Use of linearly polarized antennas in tires that constantly change position due to wheel rotation thus create problems. It is generally desirable that one of the antennas be circumferentially polarized. It is also known in the art that transmission efficiency is reduced when a transmission must pass from one material to another material. It is thus desired to position the antenna as close to the outside of the pneumatic tire as possible in order to minimize the number of material changes that the transmission experiences. In the past, the antenna of the monitoring device generally extended into the interior chamber of the tire such that the radio waves had to first pass through the air inside the tire, through the innerliner, through the tire sidewall, and then through the air to the data gathering device. It is thus desired in the art to provide an antenna for an active, self-powered programmable electronic device that is positioned and configured to maximize the probability of signal propagation through the tire sidewall.
The bead ring and apex filler of the tire tend to interfere with the radially-disposed radio transmissions from the monitoring device. It has also been found that the steel reinforcing cords of the sidewall in an off-the-road tire also interfere with the signal propagation. The metal reinforcing cords create lines of electrical interference that must be considered when designing an antenna for an electronic monitoring device for a pneumatic tire. Another problem with transmitting through a tire sidewall is that the rubber of the sidewall may include carbon material that degrades the signal propagation. Another problem with transmitting through a tire sidewall is that the power that drives the transmission is limited by government radio regulations and design consideration. Electronic monitoring devices are preferably small power sources. The amount of power to drive the transmission is thus limited and the design of the antenna must consider the limited power of the monitoring device, in order to ensure a long lifetime for said device.
In view of the foregoing, it is an objective of the present invention to provide a monitoring device and antenna configuration that maximizes the probability of signal propagation through the tire sidewall.
Another objective of the present invention is to provide a monitoring device and antenna configuration for a pneumatic tire that uses a -radial dipole antenna connected to an electronic monitoring device.
Another objective of the present invention is to provide a monitoring device and antenna configuration that orients the -radial dipole antenna orthogonally with respect to the lines of electrical interference to maximize the probability of signal propagation through the tire sidewall.
Another objective of the present invention is to provide a monitoring device and antenna configuration for a pneumatic tire where the radial dipole antenna is disposed closely adjacent the tire sidewall so that the signal propagates directly into the sidewall.
Another objective of the present invention is to provide a monitoring device and antenna configuration for a pneumatic tire that retains the antenna in a specific orientation and seals the antenna from the inside of the tire.
Another objective of the present invention is to provide a monitoring device and antenna configuration for a pneumatic tire that is of simple construction, that achieves the stated objectives in a simple, effective, and inexpensive manner, that solves the problems, and that satisfies the needs existing in the art.
These and other objectives and advantages of the present invention are obtained by a monitoring device for a pneumatic tire including at least one sensing element for sensing at least one engineering condition of the pneumatic tire; and a radial dipole antenna in electrical communication with the sensing element.
Other objectives and advantages of the present invention are achieved by the combination of a pneumatic tire; a monitoring device for monitoring at least one engineering condition of the pneumatic tire; the pneumatic tire having a sidewall; the monitoring device having at least one sensing element for sensing at least one engineering condition of the pneumatic tire; and a pole antenna in electrical communication with the sensing element.
Still other objectives and advantages of the present invention are achieved by the combination of a pneumatic tire and a monitoring device for monitoring at least one engineering condition of the pneumatic tire; the pneumatic tire having a sidewall and a plurality of reinforcing cords carried in the sidewall; a bead ring disposed in the tire sidewall; the monitoring device having at least one sensing element for sensing at least one engineering condition of the pneumatic tire; and a dipole antenna in electrical communication with the sensing element; the antenna overlying at least one of the reinforcing cords and being disposed substantially perpendicular to each of the reinforcing cords that it overlies.